J Neurol Surg B Skull Base 2014; 75 - A104
DOI: 10.1055/s-0034-1370510

Normal Dimensions of the Posterior Pituitary Bright Spot on Magnetic Resonance Imaging

Martin Cote 1, Karen L. Salzman 1, Mohammad Sorour 1, William T. Couldwell 1
  • 1Salt Lake City, USA

Introduction: The normal pituitary bright spot seen on unenhanced T1-weighted magnetic resonance imaging is thought to result from the T1-shortening effect of the vasopressin stored in the posterior pituitary. Individual variations in its size may be difficult to differentiate from pathological conditions resulting in either absence of the pituitary bright spot or in T1-hyperintense lesions of the sella. The objective of this paper was to define a range of normal dimensions of the pituitary bright spot and to illustrate some of the most commonly encountered pathologies that result in absence or enlargement of the pituitary bright spot.

Material and Methods: We selected normal pituitary MRIs from 106 patients. The size of each pituitary bright spot was measured in the longest axis and in the dimension perpendicular to this axis to describe the typical dimensions. We also present cases of patients with pituitary abnormalities to highlight the differences and potential overlap between normal and pathological pituitary imaging.

Results: All of the subjects were found to have pituitary bright spots, and the mean dimensions were 4.8 mm in the long axis and 2.4 mm in the short axis. The dimension of the pituitary bright spot in the long axis decreased with age. The distribution of dimensions of the pituitary bright spot was normal, indicating that 99.7% of patients should have a pituitary bright spot measuring between 1.2 and 8.5 mm in its long axis and between 0.4 and 4.4 mm in its short axis, an interval corresponding to three standard deviations below and above the mean. In cases where the dimension of the pituitary bright spot is outside of this range, pathological conditions should be considered.

Conclusions: The pituitary bright spot should always be demonstrated on T1-weighted MRI, and its dimensions should be within the identified normal range in most subjects. Outside of this range, pathological conditions affecting the pituitary bright spot should be considered.